Why the sound-absorbing performance of heartwood and sapwood differs in yellow poplar (Liriodendron tulipifera) cross-sections?
In this study, we investigated why the sound-absorbing performance is different with between heartwood and sapwood of yellow poplar, which are known for their sound-absorbing properties. We performed image observation as well as gas permeability, pore size, and porosity analysis, and measured the sound absorption coefficient of all samples using an impedance tube. We determined that the pores were significantly larger, and the gas permeability and through-pore porosity much higher, in the sapwood than the heartwood. The average sound absorption coefficient of the sapwood at 2000-6400 Hz (0.61 ± 0.04) was 2.7x that of the heartwood (0.23 ± 0.03). The average NRC of the sapwood (0.23 ± 0.01) was 1.9x that of the heartwood (0.12 ± 0.01). This study ultimately determined that the sapwood, as a consequence of its larger pore size and superior through-pore porosity, which thereby improved its gas permeability, outperformed the heartwood in terms of sound-absorption. We also determined that pore size and through-pore porosity were the primary parameters that determined the sound-absorbing performance of yellow poplar cross-sections.